Carpetweed- Unsightly but Not a Big Threat to Sweetpotato Fields

Stephen Meyers, Sweetpotato Extension Specialist
By Stephen Meyers, Sweetpotato Extension Specialist June 30, 2014 12:29

It’s that time in the sweetpotato production season- where the last slips are making their way into the ground and herbicide treatments applied to the earlier planted crop get tested prior to canopy closure. While pigweeds and nutsedges represent the greatest threat to yield and quality, carpetweed (Mollugo verticillata L.) appears to be the on the minds of many growers. Carpetweed is very common in sweetpotato production systems in Mississippi. Unfortunately, the herbicide used most frequently in Mississippi sweetpotato production, Command (a.i. clomazone), provides no control of the weed and in some instances seems to enhance carpetweed germination and growth.

While unsightly, carpetweed poses little threat to sweetpotato yield and storage root quality. Unlike other more troublesome weeds, carpetweed does not tend to grow above the sweetpotato canopy nor does it have an extensive root system with which to compete for water and nutrients. Some have questioned if fields with a heavy carpetweed infestation will suffer from oxygen depleted soil conditions. There is no evidence to suggest this is plausible.

Unfortunately, postemergence herbicide options in sweetpotato are limited to hooded applications of broad-spectrum herbicides between rows and broadcast applications of grass-selective herbicides. Timely cultivation remains the best means of controlling weeds present between rows, including carpetweed. Assuming all other weeds have been well controlled, cultivation should be put off until at least two weeks after transplanting. Doing so maximizes the residual activity of any pre-transplanting or early post-transplanting herbicide applications.  A post-cultivation application of Dual Magnum, if followed by an activating rainfall, will help to control weeds until vine closure.  In fields with a heavy infestation of carpetweed, one should consider the use of Valor pre-transplanting for future sweetpotato crops.

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Stephen Meyers, Sweetpotato Extension Specialist
By Stephen Meyers, Sweetpotato Extension Specialist June 30, 2014 12:29
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